Although applicable to any micromechanical components, the present disclosure and the problem addressed thereby are explained with reference to silicon-based components.
Micromechanical sensor apparatuses, for example inertial sensors, are usually realized by means of a capacitive or piezoresistive transducer. Although they have been available for some time now, sensors having a movable gate are not found on the market. A major reason for this is the production of the transducer element, in particular the provision of a suitable sacrificial layer process. Silicon oxide is usually used as a sacrificial layer in micromechanics. As a result, however, the channel region and the source/drain contacts are present in an open and unprotected manner, since the gate oxide is also inevitably removed as well when the sacrificial layer is removed. The channel region is then exposed in an unprotected manner, as are the PN junctions between source/drain and channel region. As a result, surface defects are produced which influence the operating range of the transistor or lead to drift or noise and reduce the suitability as a reliable sensor element.
EP 0 990 911 A1 describes a micromechanical sensor on the basis of the field effect transistor having a movable gate, which is movable in a direction parallel to the substrate surface, wherein the movement of the gate in this direction leads to an enlargement or reduction of the channel region overlapped by the gate in at least one MOSFET.